Once considered “the enemy of all small birds” ( Sutton 1928a ), the Sharp-shinned Hawk is a small, slender, feisty accipiter, with short, rounded wings and a long, narrow tail. Although small mammals and even insects appear in its diet, this forest-dwelling predator feeds almost entirely on small birds.
Sharp-shinned Hawks are widely dispersed and seldom-seen nesters that breed mainly in large stands of deciduous, coniferous, and mixed pine-hardwood forests and pine plantations. In temperate areas, nesting coincides with the annual peak in songbird abundance. The species' secretive nature and the dense vegetation of its nesting habitat make it difficult to find and study during the breeding season. The early stages of nesting, in particular, are little studied. The bird is best seen, and most frequently studied, on migration, when large numbers of individuals concentrate along major migratory corridors and bottlenecks, particularly in the East.
As is true of many members of the genus, the Sharp-shinned Hawk has especially long middle toes and large eyes, useful attributes for catching highly mobile prey. The species is the most sexually dimorphic of all North American raptors, with males averaging only 57% of the body mass of females ( Snyder and Wiley 1976 ).
Sharp-shinned hawks historically have been described as vicious bird killers—even by many ornithologists. In the first few decades of the twentieth century, gunners shot thousands of this species at Cape May Point, NJ; Hawk Mountain, eastern Pennsylvania; and other sites along important eastern migration corridors. Even so, the species is known for hunting songbirds in parks and near houses, and is often seen taking prey at bird feeders ( Fisher 1893c , Stone 1937 , Klem 1981 ).
Important information on migration is available from studies in Wisconsin (Mueller and Berger Mueller and Berger 1967a , Mueller and Berger 1967c , Mueller et al. 1997 ), Pennsylvania ( Bednarz et al. 1990b , Allen et al. 1996 , Viverette et al. 1996 ), and New Jersey ( Murray 1964 , Kerlinger Kerlinger 1984 , Kerlinger 1985b , Holthuijzen et al. 1985 , Niles et al. 1996 ). Detailed information on breeding biology is available from studies in Utah ( Platt 1973 ), New Brunswick, Canada ( Meyer 1987 ), and Puerto Rico ( Delannoy and Cruz 1988 ). The possible relationship between the breeding biology of this species and its extreme sexual size dimorphism is poorly understood. Future studies of migration physiology and orientation, predation ecology, and reproductive biology (particularly fledgling behavior and development) should be especially rewarding.
Common names include “Sharp-shin,” “Sharpie,” “Blue Darter,” “Little Blue Darter,” and “Bird Hawk.”